In a computer, on-state and off-state of a transistor may be represented by data, and digital data may be indicated as a binary number. Data handled by a person may be indicated as a decimal number. A decimal number is converted into a binary number and vice versa between input and output data and data processed within the computer.
Related art is disclosed in Japanese Laid-open Patent Publication Nos. 57-061333, 10-271008, 59-168543 or 2000-200174.